Are plant proteins complete or incomplete?

Answer 1

They're complete.

Protein molecules are composed of amino acids, which contain nitrogen and sometimes sulphur. Your body uses amino acids to produce new proteins and to replace damaged proteins.

Your body can synthesize most of the 21 amino acids that you need to make protein, with the exception of nine essential amino acids (histadine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine) that must come from your food.

Plants have varying amounts of protein with varying amino acid profiles, including leafy green vegetables, tubers, grains, legumes, and nuts. All the essential and nonessential amino acids are present in these foods in amounts that meet or exceed your needs.

In 1914, Thomas B. Osborne and Lafayette B. Mendel conducted studies on rats, which suggested that they grew best when fed a combination of plant foods whose amino acid patterns resembled that of animal protein. That makes sense, as all baby mammals, rats and humans included, grow best when fed the perfect food for baby mammals: their mother's milk. The term "complete protein" was coined to describe a protein in which all eight or nine essential amino acids are present in the same proportion that they occur in animals. "Incomplete protein" described the varying amino acid patterns in plants. It's a misleading term, because it suggest that humans (and other animals, one would assume) can't get enough essential amino acids to make protein from plants.

Fortunately, the theory that plant proteins are somehow "incomplete" and therefore inadequate has been disproven. All unrefined foods have varying amounts of protein with varying amino acid profiles, including leafy green vegetables, tubers, grains, legumes, and nuts. All the essential and nonessential amino acids are present in any single one of these foods in amounts that meet or exceed your needs, even if you are an endurance athlete or body builder.